In the past many boiler types of steam engines have been designed. The engines have all worked very well, so well that at the turn of the century most engines were steam engines of the boiler type. Of course in those days economy was not as important as it is now with fuel shortages in prospect. The poor efficiency of the old types of boiler steam engine were bypassed by more efficient internal combustion engines.
Recent efforts have been made to improve the efficiency of the steam engine by recovering and recompressing the steam. U.S. Pat. No. 4,104,869 is cited as an example of the new art of recovering the heat from exhausted steam and gases to produce new steam, thereafter the new steam being recompressed while the new steam is kept saturated. The engines of U.S. Pat. No. 4,104,869 are much more economical than internal combustion engines and the old type boiler steam engine.
Whereas the engines of U.S. Pat. No. 4,104,869 produce steam by direct contact and mixing with combustion gases in an external combustion chamber, this new steam engine uses a conventional boiler. Therefore, the combustion gases are not mixed with the steam as in the engines of U.S. Pat. No. 4,104,869 and do not need to be separated after expansion in a cylinder. The exhaust gases are exhausted to the atmosphere after passing through heat exchangers. Of course the steam is produced much faster in the engines of U.S. Pat. No. 4,104,869, but then the advantages of separation in a boiler are more practical in certain applications.
Another advantage of this new steam engine is that the exhaust steam is kept in a steam state before being recompressed whereas the engines of U.S. Pat. No. 4,104,869 condense the steam to water and then reheat the reclaimed water to make new steam. The advantage is that a large heat exchanger is not needed, a small one being sufficient. Another advantage is that there is no residue to be filtered from reclaimed water. The steam and water of this new engine is kept clean by separation.
Another advantage of this new steam engine is that a low pressure is all that is needed for the pressurized fuel supply and the pressurized oxygen supply. The engines of U.S. Pat. No. 4,104,869 require a high pressure for both the fuel supply and the oxygen supply. Therefore, less energy is needed to run these supplies and less expensive parts are needed in this new engine.
Being a mostly closed steam cycle, great economy can be the result in this new engine. The chief difference is that the exhaust gas contains a great deal of heat which goes to the atmosphere. Some of the exhaust gas heat is recovered in a heat exchanger whereas almost all of the gas heat is used or recovered in the engines of U.S. Pat. No. 4,104,869. Some economy is sacrificed to obtain the above advantages. Depending on the application, the advantages above greatly outweigh the disadvantage of extreme economy in the engines of U.S. Pat. No. 4,104,869.